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McQuillan et al. (Mon. Not. R. Astron. Soc. 432:1203, 2013) presented 1570 periods $P$ of M dwarf stars in the field of view of the Kepler telescope. It is expected that most of these reflect rotation periods, due to starspots. It is shown here that the data can be modelled as a mixture of four subpopulations, three of which are overlapping log-normal distributions. The fourth subpopulation has a power law distribution, with $P^{-1/2}$ . It is also demonstrated that the bulk of the longer periods, representing the two major subpopulations, could be drawn from a single subpopulation, but with a period-dependent probability of observing half the true period.

The paper describes continuous photometric monitoring of four pre-main-sequence stars, probable members of young stellar associations. Measurements, covering at least four nights per star, were obtained by cycling through several filters. The data could be used to choose between aliases of rotation periods quoted in the literature. As expected, the amplitudes of sinusoidal variations decline with increasing wavelength, mildly enough to indicate the presence of coolspots on the stellar surfaces. Variability amplitudes can dwindle from a 0.1mag level to virtually zero on a time-scale of one or two days. A flare observed in CD-36 3202 is discussed in some detail, and a useful mathematical model for its shape is introduced. It is demonstrated that accurate colour indices (σ < 5–6 mmag, typically) can be derived from the photometry. The magnitude variations as measured through different filters are linearly related. This is exploited to calculate spot temperatures (800–1150K below photospheric for the different stars) and the ranges of variation of the spot filling factors (roughly 10– 20 per cent). The available All Sky Automated Survey measurements of the stars are analysed, and it is concluded that there is good evidence for differential rotation in all four stars.

Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence companion (O'Donoghue et al. 1997), however the period and the orbit semi-major axes have not been precisely determined. This paper presents orbital characteristics of the EC 20117-4014 binary system using 20 years of photometric data. Periodic Observed minus Calculated (O-C) variations were detected in the two highest amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system's precise orbital period (P = 792.3 days) and the light-travel time amplitude (A = 468.9 s). This binary shows no significant orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3 $\sigma$ as an upper limit). This upper limit of the eccentricity is the lowest among all wide sdB binaries with known orbital parameters. This analysis indicated that the sdB is likely to have lost its hydrogen envelope through stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB stars. In addition to those results, the underlying pulsation period change obtained from the photometric data was $\dot{P}$ = 5.4 ($\pm$0.7) $\times$ $10^{-14}$ d d$^{-1}$, which shows that the sdB is just before the end of the core helium-burning phase.

Context. It is now generally accepted that the near-infrared excess of Herbig AeBe stars originates in the dust of a circumstellar disk. Aims. The aims of this article are to infer the radial and vertical structure of these disks at scales of order one au, and the properties of the dust grains. Methods. The program objects (51 in total) were observed with the H-band (1.6micron) PIONIER/VLTI interferometer. The largest baselines allowed us to resolve (at least partially) structures of a few tenths of an au at typical distances of a few hundred parsecs. Dedicated UBVRIJHK photometric measurements were also obtained. Spectral and 2D geometrical parameters are extracted via fits of a few simple models: ellipsoids and broadened rings with azimuthal modulation. Model bias is mitigated by parallel fits of physical disk models. Sample statistics were evaluated against similar statistics for the physical disk models to infer properties of the sample objects as a group. Results. We find that dust at the inner rim of the disk has a sublimation temperature Tsub~1800K. A ring morphology is confirmed for approximately half the resolved objects; these rings are wide delta_r>=0.5. A wide ring favors a rim that, on the star-facing side, looks more like a knife edge than a doughnut. The data are also compatible with a the combination of a narrow ring and an inner disk of unspecified nature inside the dust sublimation radius. The disk inner part has a thickness z/r~0.2, flaring to z/r~0.5 in the outer part. We confirm the known luminosity-radius relation; a simple physical model is consistent with both the mean luminosity-radius relation and the ring relative width; however, a significant spread around the mean relation is present. In some of the objects we find a halo component, fully resolved at the shortest interferometer spacing, that is related to the HAeBe class., 41 pages. 23 figures. Four appendices

The standard method of studying period changes in variable stars is to study the timing residuals or O−C values of light-curve maxima or minima. The advent of photometric surveys for variability, covering large parts of the sky and stretching over years, has made available measurementsofprobablyhundredsofthousandsofvariablestars,observedatrandomphases. Simple methodology is described which can be used to quickly check such measurements of a star for indications of period changes. Effectively, the low-frequency periodogram of a first-order estimate of the O−C function is calculated. In the case of light travel time (LTT) effects, the projected orbital amplitude follows by robust regression of a sinusoid on the O−C. The results can be used as input into a full non-linear least-squares regression directly on the observations. Extensive simulations of LTT configurations are used to explore the sensitivity of results to various parameter values (period of the variable star and signal to noise of measurements; orbital period and amplitude; number and time baseline of observations). The methodology is applied to observations of three previously studied stars.

A common problem in CCD photometry is to combine measurements obtained at different epochs. This is especially challenging if the fields only overlap partially, and are sparse, so that not all calibrating stars are observed at all epochs. A least-squares method for determining zero-points for all epochs under these circumstances is formulated. Allowance is made not only for the presence of intra-night measurement errors, but also for epoch-to-epoch scatter in star brightnesses (due, for example, to slow variability or instrumental effects). Expressions are derived for the uncertainties in the estimated zero-points. Three different criteria for selecting optimal calibrating subsets of the available group of stars are introduced. Simulations show that if intra-night variability dominates, it may be best to use all available stars for zero-point determinations. On the other hand, if epoch-to-epoch scatter dominates, smaller subsets of stars may give superior results. Characterization of the uncertainty in the estimated variance of epoch-to-epoch variability remains an important outstanding problem.

A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely type of K3V for the secondary star. We compare our results with atmospheric parameters derived by Fontaine et al. (2008) and in the context of existing evolution models for sdO stars. New and more extensive photometry is also presented which recovers most, but not all, frequencies found in an earlier paper. It therefore seems probable that some pulsation modes have variable amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO models show those having log g > 5.3 to be more likely to be unstable and capable of driving pulsation in the observed frequency range., 14 pages, 12 figures, accepted for publication in MNRAS, 2009 September 2

We present new UBV(RI)C photometry of 22 stars that host transiting planets, 19 of which were discovered by the Wide Angle Search for Planets (WASP) survey. We use these data together with Two Micron All Sky Survey (2MASS)JHKS photometry to estimate the effective temperature of these stars using the infrared flux method. We find that the effective temperature estimates for stars discovered by the WASP survey based on the analysis of spectra are reliable to better than their quoted uncertainties.

Multicolour time-series photometry of two newly discovered slowly pulsating sdB stars (V1093 Her stars, also known as PG 1716 stars) is described. Both stars are fairly bright and appear, from the limited amount of data, to have rich pulsation spectra. Given that the amplitudes of variation of both stars are also large compared to most PG 1716 stars, both are good candidates for extensive follow-up observations.

We present homogeneous, standardized UBV(RI)C photometry for over 700 nearby stars selected on the basis of Hipparcos parallaxes. Additionally, we list JHK photometry for about half of these stars, as well as L photometry for 86 of the brightest. A number of stars with peculiar colours or anomalous locations in various colour–magnitude diagrams are discussed.

We present photometry which shows that two known hot subdwarf stars, HE 0218−3437 and LB 1516, are variable. LB 1516 exhibits several frequencies in the range 12–25 cycles d −1 (periods of about 1–2 h) with amplitudes less than about 0.003 mag and appears to be a typical slowly pulsating sdB star. Results from a multisite campaign on HE 0218−3437 show the presence of two frequencies only, the lower amplitude variation an apparent subharmonic of the higher amplitude periodicity. It is likely that the star is in a binary system, and that the variability is due to ellipsoidal deformation of the primary star.

Most of the pulsations which have been observed in sdB stars have very low amplitudes. Detection of modes from photometric observations is usually performed by noting the most prominent peaks in a periodogram or, equivalently, an amplitude spectrum. A common strategy is to assume that peaks which exceed four times the mean noise level correspond to significant periodicities. The efficiency of the assumption is investigated by simulation. It is found that the actual significance levels corresponding to the four sigma limit may vary by orders of magnitude, depending on the exact data configuration.

JL 82 is a known binary, consisting of an sdB star and a companion which is not directly observable in the optical. Photometric measurements reported in this paper show it to variable with both the binary period (∼0.75 d), as well as on much shorter time-scales. The shorter periods are ascribed to pulsation of the sdB star, making it a member of the PG 1716 class of pulsating stars.

Systematic variability in stellar magnitudes, as derived from profile fitting to CCD images, may in some instances be due to variable seeing. It is suggested that this happens in cases where the stars are unresolved pairs, typically with sub-arcsecond separation between the components. It is shown that the fitting of suitable Generalised Additive Models to time series photometry can disentangle intrinsic stellar variability and seeing-induced brightness changes. It is possible that there will be a fixed seeing response associated with a given star which exhibits the effect: estimation of this response from several long photometric runs is demonstrated.

Summary We report the results of a period change analysis of time series observations for 378 pulsating variable stars. The null hypothesis of no trend in expected periods is tested for each of the stars. The tests are non-parametric in that potential trends are estimated by local linear smoothers. Our testing methodology has some novel features. First, the null distribution of a test statistic is defined to be the distribution that results in repeated sampling from a population of stars. This distribution is estimated by means of a bootstrap algorithm that resamples from the collection of 378 stars. Bootstrapping in this way obviates the problem that the conditional sampling distribution of a statistic, given a particular star, may depend on unknown parameters of that star. Another novel feature of our test statistics is that one-sided cross-validation is used to choose the smoothing parameters of the local linear estimators on which they are based. It is shown that doing so results in tests that are tremendously more powerful than analogous tests that are based on the usual version of cross-validation. The positive false discovery rate method of Storey is used to account for the fact that we simultaneously test 378 hypotheses. We ultimately find that 56 of the 378 stars have changes in mean pulsation period that are significant when controlling the positive false discovery rate at the 5% level.

Near-infrared photometry of 599 stars is used to calculate transformations from the South African Astronomical Observatory (SAAO) JHK system to the Two-Micron All-Sky Survey (2MASS) JHKS system. Both several-term formal regression relations and simplified transformations are presented. Inverse transformations (i.e. 2MASS to SAAO) are also given. The presence of non-linearities in some colour terms is highlighted.

We present homogeneous and standardized UBV(RI)C JHK photometry for over 100 M stars selected from an earlier paper on the basis of apparent photometric constancy. L photometry has been obtained for stars brighter than about L = 6. Most of the stars have a substantial number of UBV(RI)C observations and, it is hoped, will prove useful as red supplementary standards. Additionally, we list JHK photometry for nearly 300 Hipparcos red stars not selected as standards, as well as L photometry for the brightest stars.

It is assumed that K blocks (e.g. seasons) of observations are available, and the parameters characterizing a fixed-frequency sinusoidal variability (mean light level, amplitude, phase) are constant within each of the blocks. The paper is concerned with estimation when any combination of these parameters varies between blocks of observations. This allows observations subject to changes in mean light level, spot sizes and/or spot locations to be modelled. Objective choices between competing models, and the calculation of the standard errors of model parameters, are also dealt with. Illustrative applications to simulated and real data are given.

The literature on the $\lambda$ Boo stars has grown to become somewhat heterogenous, as different authors have applied different criteria across the UV, optical and infrared regions to determine the membership status of $\lambda$ Boo candidates. We aim to clear up the confusion by consulting the literature on 212 objects that have been considered as $\lambda$ Boo candidates, and subsequently evaluating the evidence in favour of their admission to the $\lambda$ Boo class. We obtained new spectra of $\sim$90 of these candidates and classified them on the MK system to aid in the membership evaluations. The re-evaluation of the 212 objects resulted in 64 members and 103 non-members of the $\lambda$ Boo class, with a further 45 stars for which membership status is unclear. We suggest observations for each of the stars in the latter category that will allow them to be confidently included or rejected from the class. Our reclassification facilitates homogenous analysis on group members, and represents the largest collection of confirmed $\lambda$ Boo stars known., Comment: 40 pages, 2 tables (spanning 4 pages), 0 figures. Accepted for publication in PASA. (The MN style file was used for convenience in manuscript preparation, only.)

We report the discovery of very rapid pulsations in three sdB stars from the Edinburgh-Cape blue object survey. The short periods, small amplitudes and multi-periodicity clearly establish these stars as members of the EC 14026 class. EC 11583-2708 has pulsation periods near 149, 144 and 114 s, though evidence is presented that the 149-s period is resolved into two periods at 148.87 and 148.55 s by the full photoelectric data set. The amplitudes of the detected variations are in the range 0.002-0.006 mag. The light variation of EC 20338-1925 is dominated by a period near 147 s with a very large amplitude for a variable sdB star (0.025 mag), though four other frequencies are detected with periods near 168, 151, 141 and 135 s and amplitudes in the range 0.002-0.005 mag. The third star, EC 09582-1137, displays a light curve which is virtually a textbook example of frequency beating, being produced by two pulsations of almost equal amplitude (∼0.008 mag) and periods near 136.0 and 151.2 s.

A truncated power-law distribution is fitted to the 29 largest stellar masses known in R136. Two different statistical techniques are used, with comparable results. An upper limit to the mass distribution of the order of 140-160 Mis derived, while the power-law exponent is in the approximate range 0.9-1.7. A power-law distribution with no upper limit on the mass can be rejected with considerable confidence. It is recommended that the calculations be repeated when more reliable mass estimates are available. Ke yw ords: methods: statistical - stars: early-type - stars: luminosity function, mass function - Magellanic Clouds - galaxies: stellar content.

It is assumed that O − C (‘observed minus calculated’) values of periodic variable stars are determined by three processes, namely measurement errors, random cycle-to-cycle jitter in the period, and possibly long-term changes in the mean period. By modelling the latter as a random walk, the covariances of all O − C values can be calculated. The covariances can then be used to estimate unknown model parameters, and to choose between alternative models. Pseudo-residuals which could be used in model fit assessment are also defined. The theory is illustrated by four applications to spotted stars in eclipsing binaries. Ke yw ords: methods: data analysis ‐ methods: statistical ‐ stars: variables: other.

We present new time-resolved photometry for two sdB stars, PG 0048+091 and PG 0154+182 , which clearly shows them to be rapidly pulsating stars of the “EC14026” class. In PG 0048+091 we detect, with some confidence, seven frequencies between 5252 and 9368 μHz corresponding to periods between 190 and 107 s. In PG 0154+182 , for which our data are much sparser, we identify only a single frequency near 6090 μHz (164 s). New spectroscopy, combined with archival (2MASS) infrared photometry, indicates that PG 0048+091 has a companion of spectral type near G0V–G2V, whilst PG 0154+182 has a companion of later spectral type, probably in the range G5V–K5V.

A frequency domain test statistic is applied to the full time series of brightness maxima and minima in order to test for changes in the mean pulsation periods of 382 Mira stars. The test statistic depends on two parameters that are related to the intrinsic cycle-to-cycle scatter in the period, and to the measurement error, respectively. It is shown that the former is strongly related to the mean pulsation period of the star.

Various statistical issues regarding estimation of the mean absolute magnitude of the red clump stars, using Hipparcos parallaxes, are discussed. The problem is put in the broader context of estimation of the functional dependence of the absolute magnitude on colour of local giant stars, as derived from Hipparcos observations. The methods used include calculation of the medians and modes of the absolute magnitudes of stars binned in narrow colour intervals. The modes are determined by kernel density estimation of the underlying distribution of absolute magnitudes. A weighted least trimmed squares procedure, which allows the incorporation of all information - including negative parallaxes - is described in detail. Standard errors are estimated by bootstrapping. Results are in good agreement with those of Paczynski & Stanek.

We have investigated the pulsational characteristics of the λ Bootis type star BD Phe. Detailed asteroseismological investigations have so far only been carried out for four members of this group of stars, with the number of identified frequencies in these stars ranging from four to seven. We present 30 h of UBVRI time-series photometry, together with 14 h of high-dispersion high signal-to-noise ratio spectroscopy of BD Phe. At least seven frequencies were detected. Since these are all present in independent sets of observations, we argue that the frequencies are fairly well determined despite our limited data. We present a very tentative discussion of the possible pulsation modes. Our results may be useful in the context of recently published δ Scuti pulsation models, which take into account the effects of diffusion.

Optical UBV(RI) c and infrared JHK photometry is presented of a small sample of giant stars with short periods in the Hipparcos catalogue. Observations were limited, but were sufficient to rule out most of the Hipparcos periods. Radial velocity measurement were also made for a few stars, over six successive nights. Low-level variability was detected in a few stars. It is argued that in most cases the brightness variations are primarily due to temperature changes. These findings show that high-overtone pulsations in M giant stars occur, if at all, in a far more limited number of stars than proposed in the authors' previous discussion of the Hipparcos data alone.

We present 318 high-dispersion echelle spectra and 450 UBVRCIC observations of the pre-main-sequence star V351 Orionis. These data were obtained simultaneously over a two-week period. The star is unusual in that it no longer shows the frequent sharp fadings that occurred prior to 1986. We find features characteristic of Herbig Ae stars: Hα emission, sharp and broad Na ii absorption components and weak He i absorption. The Hα profile is strongly variable with a time-scale of 1 d and normally is an inverse P Cygni profile, but on occasions overt emission disappears altogether. The equivalent widths of the sharp Na ii absorption lines have decreased quite markedly since 1995, indicating a decrease in the column density of gas in the line of sight. We also detect very weak forbidden [O i] emission. There is no evidence for veiling of the star, but a possible 1.0-d or 0.5-d period in the equivalent widths of the lines could indicate the presence of an accretion hotspot. The star is of particular interest because it is pulsating. We detect at least two periods in the light variation and a further period from the radial velocity variations. Attempts at photometric mode identification were not successful, but from the morphology of the line profiles we can identify one mode as non-radial. In addition, we see on some nights several residual absorption subfeatures moving across the line profile from blue to red. These are almost certainly caused by one or more modes of high degree (l≈8).

We present homogeneous and standardized UBV(RI) C photometry for nearly 550 M stars selected from the Hipparcos satellite data base using the following selection criteria: lack of obvious variability (no Hipparcos variability flag); δ 1.7; and V magnitude fainter than about 7.6. Comparisons are made between the current photometry, other ground-based data sets and Hipparcos photometry. We use linear discriminant analysis to determine a luminosity segregation criterion for late-type stars, and principal component analysis to study the statistical structure of the colour indices and to calibrate absolute magnitude in terms of (V - I) for the dwarf stars. Various methods are used to determine the mean absolute magnitude of the giant stars. We find 10 dwarf stars, apparently previously unrecognized (prior to Hipparcos) as being within 25 pc, including five within 20 pc.

We present our analysis of simulated data in order to derive a detection threshold which can be used in the pre-whitening process of amplitude spectra. In case of ground-based data of pulsating stars, this threshold is conventionally taken to be four times the mean noise level in an amplitude spectrum. This threshold is questionable when space-based data are analyzed. Our effort is aimed at revising this threshold in the case of continuous 90-day Kepler K2 phase observations. Our result clearly shows that a 95% confidence level, common for ground observations, can be reached at 5.4 times the mean noise level and is coverage dependent. In addition, this threshold varies between 4.8 and 5.7, if the number of cadences is changed. This conclusion should secure further pre-whitening and helps to avoid over-interpretation of spectra of pulsating stars observed with the Kepler spacecraft during K2 phase. We compare our results with the standard approach widely used in the literature., Comment: 4 pages, 2 figues, accepted to appear in MNRAS Letters

Hot subdwarf stars of spectral type B (sdBs) are evolved, core helium-burning objects. The formation of those objects is puzzling, because the progenitor star has to lose almost its entire hydrogen envelope in the red-giant phase. Binary interactions have been invoked, but single sdBs exist as well. We report the discovery of two close hot subdwarf binaries with small radial velocity amplitudes. Follow-up photometry revealed reflection effects originating from cool irradiated companions, but no eclipses. The lower mass limits for the companions of CPD-64$^{\circ}$481 ($0.048\,M_{\rm \odot}$) and PHL\,457 ($0.027\,M_{\rm \odot}$) are significantly below the stellar mass limit. Hence they could be brown dwarfs unless the inclination is unfavourable. Two very similar systems have already been reported. The probability that none of them is a brown dwarf is very small, 0.02%. Hence we provide further evidence that substellar companions with masses that low are able to eject a common envelope and form an sdB star. Furthermore, we find that the properties of the observed sample of hot subdwarfs in reflection effect binaries is consistent with a scenario where single sdBs can still be formed via common envelope events, but their low-mass substellar companions do not survive., Comment: accepted to A&A

A statistical model is formulated that enables one to analyse jointly the times between maxima and minima in the light curves of monoperiodic pulsating stars. It is shown that the combination of both sets of data into one leads to analyses that are more sensitive. Illustrative applications to the American Association of Variable Star Observers data for a number of long-period variables demonstrate the usefulness of the approach.

The American Association of Variable Star Observers supplies the astronomical community with a large data base of times of light maxima and minima of Mira (long-period pulsating) stars. Period change studies using these data invariably use either times between maxima, or those between minima. A statistical analysis based on the two-component time series of light curve rise and fall times is developed. The results, which enable one to detect changes in the shapes of light curves, are applied to observations of seven long-period variables.

We present high-resolution spectroscopic observations of 21 B-type stars, selected from the Edinburgh–Cape Blue Object Survey. Model atmosphere analyses confirm that 14 of these stars are young, main-sequence B-type objects with Population I chemical compositions. The remaining seven are found to be evolved objects, including subdwarfs, horizontal branch and post-AGB objects. A kinematical analysis shows that all 14 young main-sequence stars could have formed in the disc and subsequently been ejected into the halo. These results are combined with the analysis of a previous subsample of stars taken from the Survey. Of the complete sample, 31 have been found to be young, main-sequence objects, with formation in the disc, and subsequent ejection into the halo, again being found to be a plausible scenario.

A selection criterion based on the relative strength of the largest peaks in the amplitude spectra, and an information criterion are used in combination to search for multiperiodicities in Hipparcos epoch photometry. The method is applied to all stars which have been classified as variable in the Hipparcos catalogue: periodic, unsolved and microvariables. Results are assessed critically: although there are many problems arising from aliasing, there are also a number of interesting frequency combinations which deserve further investigation. One such result is the possible occurrence of multiple periods of the order of a day in a few early A-type stars. The Hipparcos catalogue also contains a number of these stars with single periodicities: such stars with no obvious variability classifications are listed, and information about their properties (e.g., radial velocity variations) discussed. These stars may constitute a new class of pulsators.

ABSTRA C T One of the tools used to identify the pulsation modes of stars is a comparison of the amplitudes and phases as observed photometrically at different wavelengths. Proper application of the method requires that the errors on the measured quantities, and the correlations between them, be known (or at least estimated). It is assumed that contemporaneous measurements of the light intensity of a pulsating star are obtained in several wavebands. It is also assumed that the measurements are regularly spaced in time, although there may be missing observations. The amplitude and phase of the pulsation are estimated separately for each of the wavebands, and amplitude ratios and phase differences are calculated. A general scheme for estimating the covariance matrix of the amplitude ratios and phase differences is described. The first step is to fit a time series to the residuals after pre-whitening the observations by the best-fitting sinusoid. The residuals are then crosscorrelated to study the interdependence between the errors in the different wavebands. Once the multivariate time-series structure can be modelled, the covariance matrix can be found by bootstrapping. An illustrative application is described in detail.

ABSTRA C T The Hipparcos mission discovered a few dozen M giant stars with periods P shorter than 10 d. Similar stars may be found in other large data bases of new variables (e.g., OGLE). The three possible sources of the magnitude variations ‐ pulsation, starspots and ellipsoidal deformation ‐ are discussed in general terms. The parallaxes and V 2 I colour indices are used to calculate radii and temperatures for all M giant variables with P , 100 d. Masses are estimated from the positions of the stars in a Hertzsprung‐Russell (HR) diagram, using evolutionary tracks. Using these data, it is shown that starspots can be ruled out as a variability mechanism in almost all cases, and ellipsoidal variations in about half of the stars. Pulsation in very high-overtone modes appears to be the only viable explanation for the stars with P , 10 d. Many of the stars may be multiperiodic. IRAS data are used to deduce information about reddening and circumstellar dust. The apparently low level of mass-loss, as well as the kinematics and the spatial distribution of the stars, indicates that they are from a relatively young (i.e., thin disc) giant star population.

The Tycho Epoch Photometry Annex A, a data base of photometry of more than 34 000 bright stars, has been searched for periodic variable stars with approximately sinusoidal light curves. Advantage was taken of special properties of the observing programme (photometry in two wavebands, availability of repeated measurements) to use simple but efficient variable selection criteria. Details of 70 strong candidate variables are presented.

HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am (ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with l=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes.

We report the discovery of short-period oscillations in the sdB stars PG 0911+456 and PG 1219+534, establishing them as members of the EC 14026 stars, a recently discovered class of sdB pulsators. The atmospheric parameters for both stars are also determined. The results are: periods of (148.8, 143.7, 133.5, 128.1 s), Teff ˆ 32 800 6 300 K and log g ˆ 5:76 6 0:04 for PG 1219+534; and periods of (165.7, 161.5, 155.8 s), Teff ˆ 31 900 6 200 K and log g ˆ 5:82 6 0:02 for PG 0911+456. The pulsation periods of the 11 well-studied EC 14026 stars are compared with envelope models from the recent work of Charpinet et al. With the exception of PB8783, the longest period in each star is close to the periods of the lowest-order modes in the models. Arguments are given that this is also true for PB8783, involving an increase in its surface gravity over the value derived in an earlier paper. `Correcting' the observed periods for the effects of differing surface gravity from star to star, comparison is made with pulsation models of constant surface gravity and varying effective temperature. Reasonable agreement in the width of the instability strip is demonstrated, as well as properties of its cool boundary. Overall, the class properties of the EC 14026 stars are in impressive agreement with those predicted from models based on the Fe driving mechanism. PG 1219+534 has an atmosphere much richer in He than most sdB stars and all EC 14026 pulsators seen so far. As the Fe driving mechanism operates if suf®cient heavy elements accumulate at the appropriate layer in the stellar envelope, the mechanisms (gravitational settling, radiative levitation, weak stellar winds) that give rise to this must simultaneously be able to provide large differences in the abundance of photospheric He.

Results are reported from a multi-site photometric campaign on PG 1605+072, a member of the recently discovered class of pulsating hot subdwarfs, or EC 14026 stars. The main part of the campaign covered two weeks and produced ∼ 180 h of photoelectric photometry from the five sites involved. Periodogram analysis shows that the light curve is dominated by five frequencies in the range 1.89--2.74 mHz (periods 529--365 s) with the main frequency at 2.075 76 mHz (481.75 s), though there appear to be more than 50 frequencies identifiable down to a semi-amplitude of 0.0007 (in fractional intensity) in the range 1.74--4.84 mHz (573--206 s). Compared with other pulsating sdB stars, the low gravity (log g= 5.25) and long periods indicate that the star has evolved away from the core helium-burning horizontal branch. A preliminary model of a post-horizontal-branch star with appropriate parameters yields many pulsation periods in the range 300--600 s, but detailed mode identification is not possible at present.

ABSTRA C T We present new high-speed, multisite photometric observations of the rapidly oscillating Ap star HD 119027 acquired over seven nights during 1996. A frequency analysis of these observations reveals the presence of oscillations at 1835, 1875, 1888, 1913, 1940, 1942 and (possibly) 1953 mHz. These frequencies are consistent with a spacing of either 13 or 26 mHz, depending on the reality of the oscillations at 1875 and 1953 mHz. The data in hand do not permit us to discriminate between the two possible spacings. If the smaller value of the spacing is correct, it suggests that HD 119027 is outside the main-sequence band. Two of the frequencies listed above are separated by only 1.95 mHz, suggesting that they are modes of (n; ,) and (n π 1; , ˛ 2), which in roAp stars is a quantity governed by the internal magnetic field.

ABSTRA C T The results of 37 h of high-speed photometry of KPD 2109+4401 are described. At least five periodicities in the range 182‐198 s are consistently present in the observations, with amplitudes in the range 1‐6 mmag. Results of simultaneous multicolour high-speed photometry with the Stiening photometer are also presented; these data could in principle be used for mode identification of the periodicities. The results of a preliminary study suggest that the pulsations may all be , o 1 and 2 modes. Properties of the star are compared with those of the other EC 14026 stars.